Power MOSFET with recessed field plate

• US 7,843,004 B2
• Filed: 09/25/2007
• Issued: 11/30/2010
• Est. Priority Date: 09/27/2006
• Status: Active Grant

• Current Assignee: MaxPower Semiconductor, Inc. (Vishay Intertechnology Incorporated)
• Original Assignee: MaxPower Semiconductor, Inc. (Vishay Intertechnology Incorporated)
• Inventors: Darwish, Mohamed N.
• Primary Examiner(s): Parker; Kenneth A
• Assistant Examiner(s): Jiang; Fang-Xing
• Application Number:
  US11/903,972
• Publication Number:
  US 20080073707A1
• Time in Patent Office: 1,162 Days
• Field of Search: 257/328, 257/330, 257/E29.131, 257/E29.183, 257/E29.189, 257/E29.201, 257/E29.257, 370/466
• US Class Current: 257/341
• CPC Class Codes: H01L 21/26586 characterised by the angle between the ion beam and the crystal planes or the main crystal surface
• CPC Class Codes: H01L 29/0696 of cellular field-effect devices, e.g. multicellular DMOS transistors or IGBTs
• CPC Class Codes: H01L 29/1095 Body region, i.e. base region, of DMOS transistors or IGBTs cell layout H01L29/0696
• CPC Class Codes: H01L 29/407 Recessed field plates, e.g. trench field plates, buried field plates
• CPC Class Codes: H01L 29/41766 with at least part of the source or drain electrode having contact below the semiconductor surface, e.g. the source or drain electrode formed at least partially in a groove or with inclusions of conductor inside the semiconductor H01L29/41733 - H01L29/41758 take precedence
• CPC Class Codes: H01L 29/42368 the thickness being non-uniform
• CPC Class Codes: H01L 29/66734 with a step of recessing the gate electrode, e.g. to form a trench gate electrode
• CPC Class Codes: H01L 29/7808 the other device being a breakdown diode, e.g. Zener diode
• CPC Class Codes: H01L 29/7809 having both source and drain contacts on the same surface, i.e. Up-Drain VDMOS transistors
• CPC Class Codes: H01L 29/7813 with trench gate electrode, e.g. UMOS transistors trench gate electrodes per se H01L29/4236

Abstract

A trench MOSFET contains a recessed field plate (RFP) trench adjacent the gate trench. The RFP trench contains an RFP electrode insulated from the die by a dielectric layer along the walls of the RFP trench. The gate trench has a thick bottom oxide layer, and the gate and RFP trenches are preferably formed in the same processing step and are of substantially the same depth. When the MOSFET operates in the third quadrant (with the source/body-to-drain junction forward-biased), the combined effect of the RFP and gate electrodes significantly reduces in the minority carrier diffusion current and reverse-recovery charge. The RFP electrode also functions as a recessed field plates to reduce the electric field in the channel regions when the MOSFET source/body to-drain junction reverse-biased.

Claims

1. A MOSFET formed in a semiconductor die comprising:

a gate trench extending from a surface of the die, the gate trench comprising a gate electrode, the gate electrode being insulated from the die by a first dielectric layer, the first dielectric layer comprising a first section at a bottom of the gate trench and a second section at a sidewall of the gate trench, the first section being thicker than the second section;

a first recessed field plate (RFP) trench extending from the surface of the die, the first RFP trench containing a first RFP electrode having an upper surface which is recessed below an upper surface of said gate electrode and which is insulated from the die by a second dielectric layer;

a second RFP trench extending from the surface of the die, the second RFP trench containing a second RFP electrode which is also insulated from the die, the gate trench being located between the first and second RFP trenches;

a mesa of the die between the gate trench and the first RFP trench;

a source region of a first conductivity type in the mesa adjacent to the surface of the die and a sidewall of the gate trench;

a body region, having a second conductivity type opposite to the first conductivity type, adjacent to the sidewall of the gate trench and to the source region;

a body contact region, abutting said first and second RFP trenches and said body region,

which is at least partly self-aligned to at least one of said RFP electrodes,

which is doped with said second conductivity type,

which has a doping concentration greater than that of said body region, and

which defines a bottom junction depth which is deeper than a bottom junction of said body region; and

a drain-drift region of the first conductivity type adjacent to the body region;

wherein the respective bottoms of the first and second RFP electrodes are located at a level deeper below the surface of the die than a bottom of the gate electrode.

2. The MOSFET of claim 1, wherein the gate trench is equidistant from the first and second RFP trenches.

3. The MOSFET of claim 1, wherein a doping concentration of the drain-drift region in an area between the first RFP trench and the gate trench is less than a doping concentration of the drain-drift region in an area below the gate trench.

4. The MOSFET of claim 1, wherein the first and second RFP electrodes comprise polysilicon doped with a dopant of the first conductivity type.

5. The MOSFET of claim 1, wherein the first and second RFP electrodes comprise polysilicon doped with a dopant of the second conductivity type.

6. The MOSFET of claim 1, wherein said body contact region has a junction contour which corresponds to implantation and outdiffusion from ions introduced near the tops of said RFP electrodes.

7. The MOSFET of claim 1, further comprising metal plugs which overlie said RFP electrodes, and also a metal layer overlying said metal plugs.

8. The MOSFET of claim 1, wherein said first conductivity type is n type.

9. The MOSFET of claim 3, wherein said body contact region has a junction contour which corresponds to implantation and outdiffusion from ions introduced near the tops of said RFP electrodes.

10. The MOSFET of claim 3, further comprising metal plugs which overlie said RFP electrodes, and also a metal layer overlying said metal plugs.

11. The MOSFET of claim 3, wherein said first conductivity type is n type.

12. The MOSFET of claim 4, wherein said body contact region has a junction contour which corresponds to implantation and outdiffusion from ions introduced near the tops of said RFP electrodes.

13. The MOSFET of claim 4, further comprising metal plugs which overlie said RFP electrodes, and also a metal layer overlying said metal plugs.

14. The MOSFET of claim 4, wherein said first conductivity type is n type.

15. A MOSFET formed in a semiconductor die comprising:

a gate trench extending from a surface of the die, the gate trench comprising a gate electrode, the gate electrode being insulated from the die by a first dielectric layer, the first dielectric layer comprising a first section at a bottom of the gate trench and a second section at a sidewall of the gate trench, the first section being thicker than the second section;

a recessed field plate (RFP) trench extending from the surface of the die, the RFP trench containing an RFP electrode having an upper surface which is recessed below an upper surface of said gate electrode, the RFP electrode being insulated from the die by a second dielectric layer, a bottom of the RFP electrode being located at a level deeper below the surface of the die than a bottom of the gate electrode, the RFP electrode being electrically isolated from the gate electrode;

a mesa of the die between the gate trench and the RFP trench;

a source region of a first conductivity type in the mesa adjacent to the surface of the die, the source region extending across the mesa between a sidewall of the RFP trench and a sidewall of the gate trench;

a body region of a second conductivity type opposite to the first conductivity type in the mesa, the body region being adjacent to the source region;

a body contact region, abutting said RFP trench and said body region,

which is at least partly self-aligned to said RFP electrodes,

which is doped with said second conductivity type,

which has a doping concentration greater than that of said body region, and

which defines a bottom junction depth which is deeper than a bottom junction of said body region; and

a drain-drift region of the first conductivity type adjacent to the body region.

16. The MOSFET of claim 15, wherein a depth of the RFP trench is substantially equal to a depth of the gate trench.

17. The MOSFET of claim 15, comprising:

a second RFP trench extending from the surface of the die, the second RFP trench containing a second RFP electrode, the second RFP electrode being insulated from the die by a third dielectric layer, a bottom of the second RFP electrode being located at a level deeper below the surface of the die than a bottom of the gate electrode;

a second mesa of the die between the gate trench and the second RFP trench;

a second source region of the first conductivity type in the second mesa adjacent to the surface of the die, the second source region extending across the second mesa between a sidewall of the second RFP trench and a second sidewall of the gate trench;

a second body region of the second conductivity type in the mesa, the second body region being adjacent to the second source region and extending across the second mesa between the sidewall of the RFP trench and the second sidewall of the gate trench.

18. The MOSFET of claim 17, wherein a depth of each of the RFP trench and the second RFP trench is substantially equal to a depth of the gate trench.

19. The MOSFET of claim 15, wherein said body contact region has a junction contour which corresponds to implantation and outdiffusion from ions introduced near the tops of said RFP electrodes.

20. The MOSFET of claim 15, further comprising metal plugs which overlie said RFP electrodes, and also a metal layer overlying said metal plugs.

21. The MOSFET of claim 15, wherein said first conductivity type is n type.

22. The MOSFET of claim 16, wherein said body contact region has a junction contour which corresponds to implantation and outdiffusion from ions introduced near the tops of said RFP electrodes.

23. The MOSFET of claim 16, further comprising metal plugs which overlie said RFP electrodes, and also a metal layer overlying said metal plugs.

24. The MOSFET of claim 16, wherein said first conductivity type is n type.

25. The MOSFET of claim 17, wherein said body contact region has a junction contour which corresponds to implantation and outdiffusion from ions introduced near the tops of said RFP electrodes.

26. The MOSFET of claim 17, further comprising metal plugs which overlie said RFP electrodes, and also a metal layer overlying said metal plugs.

27. The MOSFET of claim 17, wherein said first conductivity type is n type.